In recent years, vehicles including a rear view camera system that captures an image of the rear of the vehicle using a rear camera and displays the captured image have increased with the aim of ensuring safety during reversing the vehicle. Further, with increases in the number of buyers of luxury cars, on-board cameras including a rear camera are often provided as standard equipment in pre-installed navigation systems. Meanwhile, with advancements in image recognition technology, improvements have been made in image recognition precision.
Under these circumstances, cost competition has escalated, and in a positioning technology that is an essential function of a navigation system, there is a demand for a technique with which a high level of positioning accuracy can be secured using a lower cost sensor. When complicated road conditions exist, as in Japan, it is particularly difficult to guarantee 100% positioning accuracy. For example, in gaps between buildings, multistory parking lots, elevated roads and roads running underneath, multi-level interchanges, and so on, it may be still difficult to obtain a high level of positioning accuracy using current positioning technology.
As a technique relating to this positioning technology, Patent Document 1 discloses an on-board navigation device capable of detecting a vehicle position with a high level of accuracy even when a situation in which signal reception from GPS (Global Positioning System) satellites is difficult persists. In this on-board navigation device, when a broken line is laid on a traveling road along which the vehicle is traveling, an image including the broken line is shot or photographed by an on-board camera, whereupon a broken line interval of the broken line is measured by performing image recognition processing on the image shot by the on-board camera and a number of unit lines passed by the vehicle is counted. A traveled distance of the vehicle is then calculated on the basis of the broken unit line interval of the broken line and the number of passed unit lines, whereupon a vehicle position is corrected on the basis of the calculated traveled distance.    Patent Document 1: Japanese Unexamined Patent Application No. 2006-153565
As described above, although on-board cameras have substantially become standard equipment in recent navigation systems, positioning correction using the on-board camera is not yet satisfactory. Hence, there is demand for the development of a technique for obtaining a high level of positioning accuracy by performing positioning correction using the on-board camera.